The disaster blackened beaches in five states and crippled the region's tourism and fishing industries in a tragedy that riveted the United States.

The oil giant reached a $8.6 billion settlement in 2012 with thousand of claimants but challenged the way the court calculated compensation for companies.

The US federal appeals court ruled that US district judge Carl Barbier was correct in rejecting a BP bid to require companies to prove that their losses were directly linked to the spill before getting a payout.

The plaintiffs were quick to hail the decision.

"Today's ruling is an enormous victory for the Gulf and an important step forward in ensuring that every eligible claimant is fully compensated according to the objective, transparent formulas spelled out in the settlement agreement that BP co-authored and agreed to," lawyers Steve Herman and Jim Roy said in a statement.

BP said it would weigh its options to press for clarification from the courts on the minimal requirements for plaintiffs to qualify for loss claims.

"BP will continue to press its position on the proper interpretation of the settlement agreement's provisions requiring a causal nexus between a claimant's injury and the spill," BP senior vice president of US communications Geoff Morrell said.

Judges hose down BP's objections

In its 48-page decision, a divided three-judge panel of the appellate court said that it could not agree with arguments raised by BP and other appellants and affirmed Judge Barbier's initial ruling in 2012.

"Neither class certification nor settlement approval are contrary to Article III in this case," it added, referring to federal law.

One of the judges, Emilio Garza, disagreed.

"Whether a class member was economically injured is immaterial if that loss was not caused by the oil spill," Judge Garza said in a 14-page dissent.

In December, Judge Barbier said the 2012 settlement negotiated with US authorities and accepted by BP presumed an oil spill link for any losses to businesses within certain geographical zones and in certain sectors.

Several groups of plaintiffs had previously complained after Judge Barbier's final approval of the settlement in which he certified the case as a class-action lawsuit.